This invention relates to a circuit arrangement for operating a lamp, comprising
supply input terminals for connection to a supply voltage source, PA1 a transformer provided with a primary winding L1 and a secondary winding L2, PA1 a first branch comprising terminals for holding the lamp and connecting a first end of the secondary winding L2 to a second end thereof, PA1 a second branch comprising a series circuit of a switching element and the primary winding L1 which interconnecting the supply input terminals, PA1 a control circuit coupled to a control electrode of the switching element for generating a control signal for rendering the switching element conducting and non-conducting, and thus generating a first current in the primary winding L1 and a second current in the secondary winding L2. PA1 a secondary winding L3 forming part of the transformer, PA1 a third branch comprising the terminals for holding the lamp and second diode means, and connecting a first end of the secondary winding L3 to a second end, PA1 switching means which form part of both the first and the third branch, PA1 control means coupled to a control electrode of the switching means for adjusting the conductivity state of the switching means at each change in polarity of a portion of the lamp current generated from the first current such that only one of the secondary windings is conductively connected to the terminals for holding the lamp.
Such a circuit arrangement is known from U.S. Pat. No. 5,072,155. In the known circuit arrangement, the lamp is coupled to the secondary winding L2 of the transformer during lamp operation, and the current through the lamp is generated from the second current. The power dissipated by the lamp may be adjusted over a comparatively wide range in that the frequency and/or the duty cycle of the control signal is adjusted. A disadvantage of the known circuit arrangement, however, is that the first current is comparatively great, so that the switching element must be dimensioned for passing a comparatively great current. This renders the known circuit arrangement comparatively expensive.